1. Field of Invention
The invention relates to an ink-jet head for printing by ejecting ink onto a record medium, and to an ink-jet printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink, which is supplied from an ink tank, to pulse pressure chambers. The ink-jet head selectively applies pressure to each pressure chamber to eject ink through a nozzle connected with each pressure chamber. As a means for selectively applying pulse pressure to the pressure chambers, an actuator unit or the like may be used in which ceramic piezoelectric sheets are laminated. The printing operations are carried out while reciprocating such a head at a high speed in the widthwise direction of the paper.
As for an arrangement of the pressure chambers in such an ink-jet head, there is a one-dimensional arrangement in which pressure chambers are arranged in, e.g., one or two rows along the length of the head, and a two-dimensional arrangement in which pressure chambers are arranged in a matrix along a surface of the head. To achieve high-resolution and high-speed printing, the two-dimensional arrangement of the pressure chambers is more effective. As an example of an ink-jet head in which the pressure chambers are arranged in a matrix along a surface of the head, an ink-jet head is known in which a nozzle is disposed at the center of each pressure chamber in a view perpendicular to the head surface. In this case, when pulse pressure is applied to a pressure chamber, a pressure wave propagates in the pressure chamber perpendicularly to the head surface. Ink is then ejected through the corresponding nozzle disposed at the center of the pressure chamber in a view perpendicular to the head surface.
In the above-described construction in which a nozzle is disposed at the center of each pressure chamber in a view perpendicular to the head surface, the width of a common ink passage for supplying ink may be restricted by each interval of nozzles corresponding to neighboring pressure chambers. This occurs because the common ink passage must be disposed so as not to overlap the nozzle at the center of each pressure chamber in a view perpendicular to the head surface. Besides, in this case, if nozzles are arranged at a high density to meet the demands of high-resolution and high-speed printing, the arrangement may restrict the width of the common ink passage. If the width of the common ink passage is thus restricted, the passage resistance of the common ink passage to ink is high. Thus, the smoothness of the ink supply corresponding to the maximum ink ejection cycle can not be intended.